Bamboo: Remarkable Giant Grasses

Bamboos are widespread throughout the Old and New World tropics, with one species (Arundinaria gigantea) native to the United States. In California, the naturalized giant reed (Arundo donax) is often referred to as a bamboo, but is usually classified in the arundo tribe (Arundineae) along with common reed (Phragmites australis) and pampas grass (Cortaderia). Sugar cane (Saccharum officinarum), a large, woody grass with C-4 photosynthesis, belongs to the andropogon tribe (Andropogoneae) along with corn (Zea mays) and Job's tears (Coix lacryma-jobi). Another large grass called wild cane (Saccharum spontaneum) is naturalized in the Hawaiian Islands. Unlike members of the andropogon tribe with C-4 photosynthesis, all species of the bamboo tribe (Bambuseae) and arundo tribe have C-3 photosynthesis (Walters and Keil, 1996).

Bamboos typically form dense, impenetrable clumps or spread by creeping rhizomes. Clumping bamboos are mostly native to tropical contries, such as Indonesia, Burma, Brazil, Colombia, Ecuador, India, Thailand and southern China. A few "mountain bamboos" from the Himalayas and the Andes are "temperate clumpers" that can survive in areas with freezing winters. Running bamboos are mostly from temperate climates of Japan, northern China, Siberia and one native species in the United States. Bamboos range in size from low, shrubby forms only ten feet (3 m) tall to towering giants over 100 feet (30 m). Aerial stems (called culms) develop from scaly, underground stems called rhizomes that bear roots at the nodes where the leaflike scales are attached.

Clumping bamboos, such as the large genus Bambusa, develop from branched clusters of short, "pachymorph" rhizomes that turn upward as soon as they are formed, each rhizome developing into a new culm close to the parent plant. Running bamboos, such as the genus Phyllostachys, develop from long, slender, "leptomorph" rhizomes that grow horizontally under the soil. These bamboos send up aerial culms from buds that develop at intervals along the rhizome, behind the continually growing rhizome tip. Rhizomes of running bamboos can grow more than thirty feet in one year. Entire hillsides of this type of bamboo can develop asexually from a single ancestral rhizome. In fact, the dense forests of Phyllostachys nigra in the rain forest of east Maui represent massive clonal colonies. This Chinese species was first collected on the island of Oahu in 1951.

Like most other grasses, bamboos grow and flourish until they are ready to flower; then they produce seeds and die. Because bamboos flower so infrequently, they are usually propagated vegetatively. Running bamboos are usually propagated by cuttings of the rhizome, with some buds and culms attached. Clumping bamboos can be propagated by taking a piece of a culm with at least one node and planting it in damp soil. The cut stem will develop roots at the node and produce new rhizomes and culms. Therefore, most varieties of bamboos in cultivation are clones derived from a single plant that may be traced back to one seed. This may explain why some cultivated bamboos have the same flowering cycle and mortality as populations on different continents. It should be noted here that the majority of bamboo species are not monocarpic, i.e. they do not flower gregariously and then die.

Aerial culms of bamboo are hollow except at the nodes where lateral buds and leafy branches develop. Monocot stems, such as bamboo and palms, do not have a vascular cambium and do not exhibit secondary growth by the production of concentric annual rings. They cannot increase in girth by adding lateral layers of cells as in conifers and woody dicots. Instead, they have scattered vascular bundles composed of xylem and phloem tissue, each bundle surrounded by a ring of cells called a bundle sheath. The maximum diameter of bamboo stems is predetermined at the time of sprouting (see below). Unlike bamboo and most monocots, palm stems can grow in girth by an increase in the number of parenchyma cells and vascular bundles. This primary growth is due to a region of actively dividing meristematic cells called the primary thickening meristem that surrounds the apical meristem at the tip of a stem.

The structural strength and hardness of bamboo stems is due to masses of heavily lignified tracheids and fibers associated with the vascular bundles. The wood (xylem) of conifers and dicot trees is composed of concentric layers of dense, lignified cells containing cellulose and lignin in their secondary walls. In addition to cellulose and lignin, the thick-walled fibers of bamboo also contain up to five percent silica in the form of silicon dioxide (SiO₂). Although bamboo culms do not have the structure of true wood, they are very hard because they contain silica and lignin.

As stated above, the diameter of a bamboo stem is essentially determined at the time of sprouting. The actual diameter depends on the exact species of bamboo. Just below the growing point (apical meristem) is an active region of cell division and differentiation that is responsible for the predetermined size of bamboo shoots. When a bamboo shoot emerges from the soil it consists of a series of tightly overlapping protective sheaths surrounding the developing nodes and internodes (each sheath enveloping the culm and internodes above it). The culm sheath terminates in a leaf blade that typically extends away from the culm. In bamboo shoots, the greatly reduced leaf blade is represented by a small, pointed protrusion of the sheath. Between the sheath and blade, many species have a scalelike ligule and earlike projections called auricles. The ligule and auricles may be fringed with minute bristles. All the leaf-bearing nodes are predetermined in the shoot, which grows out telescopically as the internodes elongate. This is similar to the extension of the legs of a camera tripod or the sliding tubes of a collapsible telescope or radio antenna.

If a bamboo shoot is cut off before it has begun to elongate, the culm dies. If it is cut after the culm has started to develop and elongate, it will branch out from the nodes and produce new foliage. Herbaceous grasses, such as cultivated cereals and naturalized weeds, continue to grow even after mowing. This is explained in the following section.

Bamboos are very important plants, both ecologically and economically. They are one of the most useful and valuable plants for people and provide the primary diet for giant pandas. Giant pandas are indigenous to mountain forests of small, cold-tolerant bamboos in the Yunnan province of southern China. Although they have a carnivorous ancestry and are members of the bear family (Ursidae), giant pandas have evolved a vegetarian diet of bamboos and eat the entire shoots, leaves and stems. The Himalayan red panda also feeds on bamboos along with a variety of other plants. It belongs to the family Procyonidae along with American racoons, coatimundis and ringtails.

Giant pandas are completely dependent on bamboo for food, and they require enormous quantities of it. Because of a rather inefficient digestive system compared with other herbivores, giant pandas may consume up to 85 pounds (38 kg) of bamboo per day. Pandas digest about twenty percent of the bamboo they consume, while cattle can digest sixty percent of their intake. Pandas will eat other species of bamboo but apparently prefer the kinds that grow wild in their native habitat, including Himalayacalamus, Fargesia, Drepanostachyum and Sinarundinaria, all native to Yunnan, Tibet, Nepal and northern India. Pandas once roamed over a wide range in southern China. Before the fertile valleys became farmland, they could move from one area to another to find a variety of bamboos. Now they are restricted to isolated mountain regions in which there are relatively few species of bamboo. This habitat isolation is a potentially serious problem when bamboo species that giant pandas depend on suddenly flower and die.

Some bamboo species bloom simultaneously and then die, a phenomenon that is still under investigation by plant physiologists. These species produce seed once in their life cycle and are termed monocarpic. Like other biological phenomena, there are exceptions to this worldwide mortality. In fact, most species of bamboo are not monocarpic. Some bamboos observed in cultivation are greatly weakened or die back following the blooming cycle, but actually recover in a few years and may even live to bloom again. With an average human life cycle of perhaps eighty years, few mortal botanists have ever followed the life cycle of a particular bamboo plant from germination to flowering! Variations in the exact flowering period for a given species have also been observed in cultivated bamboos. When cultivated bamboo species bloom precisely at the same time, they are very likely clones from an original rhizome that has been propagated vegetatively. Depending on the species, the unusual delayed blooming cycle may occur only once in a century. Even more astonishing is the fact that over huge geographic areas all the bamboo of a single species may flower and fruit at the same time, resulting in enormous grain (seed) production and widespread die-offs. When this massive die-off was observed in a panda preserve in 1983 the panda inhabitants faced starvation, while pandas on different mountains (with different bamboo species) had sufficient food. The Chinese launched a campaign to relocate about ten percent of the pandas in zoos; however, their failure to reproduce well in captivity further exacerbated the decline in panda populations. The birth of Hua Mei at the San Diego Zoo in the 1999 using artificial insemination was indeed a triumph for the panda breeding program.

Several hypotheses have been proposed to explain the ecological advantage of producing seed-bearing fruit only once in a life cycle (monocarpic) and with a long time interval between germination and death of up to 120 years. As I stated above, this phenomemon does not apply to the majority of bamboo species. One of the most plausible explanations involves a clever strategy to avoid annual seed predation by rodents, such as rats. Rodents are very fond of bamboo grains and if the seed predators were in tune with bamboo flowering and fruiting, they could easily destroy the bulk of the seed crop each year. With massive fruiting only once or twice in a century, the bamboos avoid tracking by vertebrates whose generation time is much shorter than the flowering cycle. With abundant food, the rodent population could increase substantially during the year following the bamboo flowering cycle; but for the next 30 to 60 years (or more), the rodent population would decrease and stabilize again while the bamboo populations regenerate. This strategy to avoid seed predation, and the extensive cultivation of fertile valleys between mountainous regions, has seriously threatened the panda populations in southern China.

Bamboos are very useful plants throughout the Old and New World tropics. It has been estimated that they are used by more than half of the world's human population every day. According to A. Lewington (Plants For People, 1990), more than 1000 different products are made from bamboo. Bamboo shoots are edible and are a major component of Asian dishes. Since fresh shoots are more flavorful than canned, bamboo farms have been established in the United States. In Tanzania, "bamboo wine" is made from the fermented juice of the wine bamboo (Oxytenanthera braunii). Although bamboo shoots are tender and weak, they grow very rapidly. In fact, there are records of tropical bamboos growing 100 feet in three months, an astonishing 0.0002 miles per hour! When the shoots leaf out in sunlight they become very strong and woody (lignified). Some bamboos stems have the same tensile strength as certain types of steel and are used to reinforce concrete. After about ten years the stems begin to deteriorate in humid tropical regions. Bamboo canes are used to make cooking utensils, blow guns, toys and furniture. Bamboo pulp is used to make paper, and small, polished stem segments are sometimes used in necklaces.

The wooden sword called a "shinai" used in the Japanese martial art of kendo is made from longitudinal strips of strong bamboo culms. Several strips are tightly bound together with string. There are many weapons made from bamboo, including bows and arrows and sharpened bamboo stakes. In Sumatra, native hunters fashion blowguns (blowpipes) from bamboo culms to shoot deadly poison darts.

Strong swords made from bamboo culms are used in the ancient Japanese martial art of kendo.  The objective is to score points by striking your opponent's head, arms and torso in strategic places.  The opponents wear heavy, protective armor. See Animated Kendo Image

Along with palms, bamboos are one of the world's most important building materials, particularly in areas where timber trees are in short supply. Large timber bamboos, including Dendrocalamus giganteus and Bambusa oldhamii are used for scaffolding, bridge-building, water pipes, storage vessels and to build houses. In fact, as a building material bamboo plays an important role in almost every country in which it occurs. In Burma and Bangladesh, about fifty percent of the houses are made almost entirely of bamboo. In Java, woven bamboo mats and screens are commonly used in timber house frames. With modern polymer glues and bonding cements, bamboos are made into plywood, matboard and laminated beams.

For centuries, Marsh Arabs of Iraq have constructed their houses entirely from bamboo-like grasses called reeds, including Phragmites australis and Arundo donax. The name Canebrake Canyon in San Diego County is derived from the common reed (Phragmites australis). This native grass may be the most widely distributed of all vascular seed plants. Where wood is scarce, bundles of reeds are used for various mud constructions, such as arches. Long after the reeds have rotted away, the arch made of layers of baked mud, still stands. One of the oldest arches in the history of architecture at Gesiphon near the site of the ancient city of Babylon is still standing, its baked bricks are more than 2,000 years old.

Bamboo has been a major building material for boats in China for countless centuries. In fact, the sectioned culms which divide the stem internodes into separate compartments may have given early boat-builders the idea of making water-tight bulkheads. Many of the junks, sampans and rafts that navigate the vast waterways of China are constructed partly or entirely of bamboo. Grass-like members of the sedge family (Cyperaceae) have also been used to make sea-worthy boats, including papyrus (Cyperus papyrus) and bulrushes of the genus Schoenoplectus. For centuries Oru Indians of Lake Titicaca in Bolivia have made boats from totora reeds (Schoenoplectus tatora). Four long bundles of reeds which taper at both ends are firmly bound together with strong ichu grass (Stipa ichu). Even the sails are made of from totora reeds which have been split and sewn together lengthwise. In his book, Sea Routes to Polynesia (1968), Thor Heyerdahl postulated that sweet potatoes were carried across the Pacific by Peruvian Indians before Europeans began to sail the world's oceans. He tested his hypothesis in 1947 by sailing a balsa wood raft, the Kon-Tiki, fashioned after the reed rafts of the Oru Indians living on Lake Titicaca in Bolivia. Although Heyerdahl's hypothesis about the transoceanic exchange of sweet potatoes by skillful pre-Columbian sailors remains an enigma (at least to some skeptics), his New World origin for the coconut has been rejected by most botanists.

Reeds and bamboos are very significant plants in the development and evolution of musical wind instruments. The variety of flutes and panpipes used by Andean musicians of Peru, Bolivia and Ecuador are made from native bamboo species, including the genus Chusquea and the pantropical reed Arundo donax. Different lengths and widths of the hollow culms produce the light airy sounds of small sikus or zampoñas and the deep bass notes of Bolivian toyos. Some of the world's most beautiful music is produced by these relatively crude instruments. Panpipes have also been made in France and the Balkan countries, primarily from the reed Arudo donax collected in marshlands of the Danube delta.

The best "reeds" for clarinet and oboe mouthpieces also come from Arundo donax. This grass is naturalized throughout the world, including river valleys and creeks of San Diego County. Often called giant reed, it spreads by thick scaly rhizomes, forming impenetrable thickets of bamboo-like stems. In fact, giant reed can literally overtake other native species in riparian habitats and is considered one of the most serious weeds in California. According to W.W. Robbins, et al. (Weeds of California, 1941), giant reed was so plentiful along the Los Angeles River in the early 1800s that it was gathered for roofing material and was preferred over the native tules (Scirpus californicus). Because of its invasiveness, drastic control measures have been used in San Diego County, including burning and herbicide sprays.

Bamboos have also been used for wind instruments in Asian countries. The national instrument of Japan, the shaku hachi, is made from the lower end of small-culmed bamboos. The Chinese xiao, a notched flute played in modern orchestras, is made from the bamboo Phyllostachys nigra. In the Philippine city of Las Piñas, each of the 950 pipes of a remarkable organ is made from hollow bamboo culms; in Java, more than twenty percussion, wind and string instruments are made from bamboos, mostly from the genus Gigantochloa; and in Bali, the fungklih xylophone has keys made from bamboo.